The present invention relates to the data processing arts. It finds particular application in conjunction with a 90.degree. change in orientation of image data between an image or print memory and a high-speed printer and will be described with particular reference thereto. It is to be appreciated, however, that the invention will also find application in the rotation of bit map data for display and other purposes.
Heretofore, image data manipulation systems have been created which enable data to be printed in either a portrait format (long edge of the paper vertical) or a landscape format (long edge of the paper horizontal). Typically, images to be printed are stored with an organization dedicated to one of these formats. Printing the data in the other format requires rotating the image 90.degree..
Data stored in a bit map in a first print or image memory has been operated upon by a transform operation as it moves from the first image memory into a second image memory. More accurately, the data addresses were transformed such that as the data is transferred to memory cells in the second memory, the stored image is 90.degree. rotated relative to the image in the first. Although a 90.degree. rotation is most common, transforms are readily selectable which would rotate the data through any arbitrary angle. When the entire bit map had been rotated and stored in the second image or print memory, the data was transferred to the printer. See, for example, U.S. Pat. No. 4,841,453 to Finlay.
A primary drawback of rotating or otherwise transforming the data as it is moved from one image memory to another is its slowness. The print operation cannot begin until the transformation and movement of data is completed. Thus, after every sheet is printed, the printer must be stopped while the data of the next image is transformed and moved between the memories. Another drawback of this system is in the hardware overhead. Two image memories, typically VRAM's, are required. In high-resolution printing in which there are 300 bits per inch in each direction, large image memories and long transform times have been required. These common problems are compounded in larger sized drawings, such as a B size drawing which is twice the size of a conventional A size letter page or a C size drawing which is twice the size of a B size drawing.
It might be noted that in word processing applications, letter information is communicated by fonts. To perform the 90.degree. rotation, the font or bit map representing each letter must be rotated 90.degree. and the position of the font on the sheet must be transformed. This creates a more complex transformation procedure which tends to slow the transfer of image data between the two memories. See, for example, U.S. Pat. Nos. 4,931,960 and 4,843,405 to Morikawa, et al., and U.S. Pat. No. 4,635,212 to Hatazawa.
It has been recognized that expediting the transform operation would be advantageous. Expeditious data address transform techniques are disclosed in U.S. Pat. No. 4,716,544 to Bartley and U.S. Pat. No. 4,727,497 to Peters, et al.
The present invention contemplates a new and improved image data handling technique in which the address transformation and a full second memory buffer are eliminated.